Portable space heater

ABSTRACT

A compact, portable, electric space heater has a convoluted heating element providing uniform heat over a large surface area enclosed in a shell having an air inlet and an air outlet. The convoluted heating element comprises an elongated heating strip having a conductive layer provided with elongated electrodes at the opposite longitudinal edges thereof. Mounting means in the form of a pair of open spider rings respectively engaging the opposite edges of the strip support the heating element within the shell. A high capacity blower is mounted on one of the rings for circulating air over the heating element. The heating element is at least two inches wide and has a resistance between about 20 to about 200 ohms per square.

United States Patent Gartner Nov. 27, 1973 [5 PORTABLE SPACE HEATER 2,849,589 8/1958 Lancaster 219 363 1,978,413 10/1934 Child 219/370 X [75] Inventor: William JsePh Game", 1,914,724 6/1933 Johnson 219/375 B t 3,265,865 8/1966 Hagar 219/549 "[731 Aiiigiiw ,Wiiiiiiii R-nsiiiiiiii Richard 7323123 31132; Exists: :11: 513333; Franklmi both New Castlei 2,429,733 10/1947 Trent 219/369 [22] Filed: Oct. 27, 1971 Primary Examiner-A. Baths [211 APPL 193,058 Attorney-Max Dressler et al.

[52] US. Cl 2 l9/366,'219/37l, 219/375, [57] ABSTRACT 219581 219532 338/212 338/280 A compact, portable, electric space heater has a con- 51 Int. Cl 1105b 3/02, 2411 3/04 voluted heating element providing uniform heat over a [58] new of Search 219566-370 3 large surface area enclosed in a shell having an air 219,528 549i 381i 382i 532; 117/218; inlet and an air outlet. The convoluted heating ele- M. ment comprises an elongated heating strip having a conductive layer provided .with elongated electrodes [56] References C'ted at the opposite longitudinal edges thereof. Mounting UNITED STATES PATENTS means in the form of a pair of open spider rings re- 424,921 4/1890 Capek 219/375 UX spectively engaging the opposite edges of the strip 7i 60,076 5/1904 Leonard," 219/375 UX support the heating element within the shell. A high 1,633,573 1927 Daniel s i s 2l9/37I capacity blower is mounted on one of the rings for cir 1,828,809 10/1931 Landls 219/371 x culating air over the heating element. The heating elev g x ment is at least two inches wide and has a resistance 1 ran 1n... 3,651,304 3/197/2 Fedor 219 375 x belwee abut 20 to about 0 ohms per square. 1,995,673 3/1935 Evans 219/376 X 6 Claims, 7 Drawing Figures 3,041,569 6/1962 Werker 219/375 UX I 3,086,187 4/1963 Duggan et a1 219/375 UX 1 \lllll 1| Hill PAIENIEnw/mzs I SHEET FIG.

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, INVENTOR WILL/AM J. 64 T/VE/P g. ,4

ATTORNEYS PORTABLEJSPACE I SUMMARY OF THE INVENTION This invention relates to portable electrical space heaters .and to heating elements suitablefor such heat- *ers.

Electrical space heaters are commonly used to provide auxiliary heating in residential rooms and other enclosed spaces. In the most compact of such heaters, heat is generated in a resistance element'brought to red heat by 'thepassage of electrical current therethrough. The 'heatis then disseminated into the room by radiation, directed by asuitable reflector. The reflectors in such heaters are generally concavely curved to concentrate the :radiation within a relatively small sector because unconcentrated radiation ifalls away in intensity to the extent of the square .of'the distance from the-radiation source. Heatersutilizingsuch curved reflectors are inherently unable toprovide uniform heating within a room because most of the heat generated is disseminated in a relativelysmall'sector along the axis of the curved reflector and relatively little heat is dissemi- "na ted elsewhere. v

In some compact electrical heaters, a fan of low capacity is provided which directs=a small streamof air into contact with the heated surface of the reverse (convex) side of the reflector and thence out of the heater and into the room. Such a 'fan provides a limited amount of heat dissemination by convection and thereby improves somewhat the uniformity of total heat dissemination within the room. However, the fans in such heaters 'must be small and must be positioned to direct an air stream against the reverse side of the reflectors. The fans cannot direct air streams against the front side of the. reflectors, or against the resistance elements themselves, because :the resistance elements are at red heat and would break if subjected to a blast of air. Thus, it has not been possible to obtain in a compact electrical heater, a high volume air flow such as would be necessary to provide effective heat dissemination by convection. I

In addition, such radiation electrical heaters are not as compact as desirable and operate at skin temperatures of the order of about 300 to 350F., temperatures high enough to cause painful burns to a crawling infant or an animal.

In accordance with the present invention, a highly compact electrical heater is provided which disseminates its generated heat with a high volume of air and which operates at moderate skin temperatures of the order of about 130 to 140F., which temperatures are harmless to normal contact.

Specifically, a compact portable space heater is provided comprising a partially open outer wall to permit air passage therethrough into and out of said shell, an elongated, convoluted heating strip rigidly supported within said shell and spaced therefrom substantially through its length and a blower rigidly supported within said shell at a location in open communication with said heating strip, said heating strip comprising a thin conductive layer having a width of at least two inches, having elongated electrodes at its opposite edges and having a resistance between about 20 and about 200 ohms per square. The heating strip may be convoluted into any shape which substantially fills the crosssectional space within the outer wall and is generally convoluted so that a straight line connecting two points widelyspaced along said strip will intersect the strip a plurality of .times. ln a preferred embodiment the convoluted configuration in a spiral.

DESCRIPTION OF SPECIFIC EMBODIMENT The invention is best understood by reference to the drawings of which:

FIG. 1 is a perspective view of the portable heater of this invention in one embodiment;

FIG. 2 is an enlarged elevation, partially in section;

FIG. 3 isa horizontalsection through the heating unit assembly of FIG. 2;

FIGS. 4 and 5 are plan views of alternate embodiments of different convoluted configurations of the heating element;

FIG. 6 is a detail of the heating strip in an extended, unconvoluted state, partially stripped to show its layered structure and its wiring; and

FIG. 7 is a plan view in section of an alternate embodiment of the heater of this invention adapted to be positioned in the corner of a room.

As'seen in FIG. 1 and 2, the heater comprises shell 11 made up of cylindrical side wall 12 and top and bottom circular closures 13 and 14, respectively. Shell 11 is partially open, being provided with air outlet 16 between the periphery of top closure 13 and the upper end of side wall 12 and air inlet 17 between the periphery of the bottom closure 13 and the lower end of side wall 12 to permit ingress and egress of air to and from the interior of the shell.

Within the shell and rigidly positioned by lower support ring 18 and upper support ring 19 is heating unit assembly 21 (shown in FIG. 3 in horizontal cross section), comprising elongated heating strip 22 convoluted into a spiral configuration which is held in position between upper and lower support members 23 and 24, each comprising a spider ring having six spokes, generated at hollow core 26 and terminating at rim 27. Each spoke is transversely grooved to provide guides for the edges of strip 22 so that it may be held in spiral position. Rim 27 defines an incomplete circle to provide space within the shell for switch 28, the external portion of which is shown in FIG. 1. In the heating unit assembly, support rings 18 and 19 are held together after assembly by hollow tube 29 which is flattened at each end under heat and pressure to provide rivet-like heads. I

The heating strip is a flat strip about 6 inches wide and about 44 inches long. As shown in FIG. 6, it comprises a conductive layer 31, sandwiched between upper and lower sheets, 32 and 33, respectively, of asbestos paper. Along the upper edge of strip 22, between conductive layer 31 and lower sheet 33, is an electrode 34 in the form of an elongated strip of copper foil. Electrode 36, also of copper foil is similarly situated along the lower edge of strip 22, except that electrode 36 is separated at gap 37 into two unequal portions, the left portion (as shown in FIG. 6) comprising about 80 percent of the total length. Lead wire 38 is attached to electrode 34 and lead wire 39 of opposite polarity is attached to the left end of electrode 36. Lead wire 41 of the same polarity as lead wire 39 is attached to the right end of electrode 36; and the wiring through I ment the heater operates at 1,400 watts when current (at 120 volts) flows only through wires 38 and 39, and at 1,750 watts when current flows through all three lead wires. The circuit through lead wires 38 and 39 includes a high limit thermostat (not shown), serving as a safety feature to shut the unit off if the temperature within the shell reaches an unacceptable level (e.g., 200F.), and an adjustable thermostat (not shown) to operate or shut the unit off in response to the temperature of the incoming air.

The nature of the conductive layer, per se, and the nature of the heating element, per se, are not part of this invention since such layers and such elements are described in the prior art, as for example, in U.S. Pat. Nos. 2,991,257, 2,803,566, and 3,179,544.

As is known, such conductive layers can be tailor made, within a broad range, to any desired level of resistance by varying the proportions of conductive and non-conductive particles and/or the thickness of the layer. Greater amounts of non-conductive material, lesser amounts of conductive material and lesser thicknesses are conductive to higher resistance.

U.S. Pat. No. 3,179,544 is particularly relevant since it describes a conductive layer in a preformed structure sandwiched between a supporting insulating base and a covering insulating layer and containing two electrode strips, each running the entire length of the preformed structure, one near each edgeof the conductive layer. Preformed structures of the nature of those disclosed in U.S. Pat. No. 3,179,544, where both the insulating base and insulating layer may be made of ashes tos paper, are particularly useful as the heating elements of this invention.

The conductive layer should be of such character that it provides between about 20 and 200 ohms of resistance per square. Generally, the higher resistances within this range are used at higher line voltages. For line voltages of about 120 volts, and wattages of the order of about 1,400 l,700 watts a suitable range of resistance values if from about 50 to about 100 ohms per square, and preferably from about 60 to about 80 ohms per square.

When switch 28 is in its on position at either the lower or higher wattage level, current, is also provided to fan motor 42 which is wired in parallel to the heater strip. The lead wires to the fan pass through the hollow center of tube 29. The fan motor operates fan 43, a relatively large fan, typically a fan rated at 250 cubic feet per minute in free air, although its actual air movement rate within the partial enclosure of shell 11 is substantially less. Fan 43 draws air through lower openings 17 and past the large heated surface of the convoluted heating strip and then pushes it out through upper openings 16. Openings l7 and 16 in this embodiment extend completely around the circumference of the shell, providing for both intake and exhaust over a 360 range. I

By reason of the large available heating surface strip 21, the incoming air is rapidly heated despite the fact that the surface temperature of the heating strip is, at

most, about 275F. Typically, the heater can raise the ing effect of the heater rapidly and to provide relatively uniform temperatures within the enclosed space to be heated. 1

In the preferred embodiment of FIGS. 1 to 3 the heating element is convoluted into a spiral pattern. Such a pattern substantially fills the cross-sectional space within the shell of the heater to provide a large surface area within a compact space. A straight line connecting two points widely spaced along the heating strip (as, for example, points A and B of FIG. 3) will intersect the strip a plurality of times (as shown by the dotted line connecting points A and B).

If desired, other convoluted shapes may be used in place of thespiral configuration. FIG. 4 shows a heat ing strip in the form of a single zigzag convoluted so that a straight line between points C and D intersect the strip a plurality of times (as shown by the dotted line); and FIG. 5 shows a heating strip in the form of a double zigzag so that a straight line between points E and F intersect the strip a plurality of times (as shown by the dotted line). The configurations of FIGS. v4 and 5 may be used for heater shells of square or rectangular cross section, or may be used for shells of other crosssectional configurations, particularly where the length of successive zigzag salients may vary.

The heater of this invention is easily and inexpensively fabricated since the shell and interior structural parts can be made of injection molded plastics. Conventional space heaters must be made of metal because of the high temperatures involved in their operation.

In the manufacture of the heater of FIGS. 1 to 3, a prewired heating strip is wound into a spiral configuration by positioning its edges into the appropriate grooves in the spokes of the upper and lower support members. Hollow tube 29 is then inserted through the center of each of the support members and flattened under heat and pressure to provide rivet-like heads holding together the heating unit pre-assembly. The fan and switches are then assembled to the heating unit and wired; and the entire assembly is placed within a semicylindrical half of side wall 12. Then the second half of side wall 12 is placed in position to complete the cylindrical wall and top and bottom closures l3 and 14 are used to cap each end of the cylindrical wall and to hold it together. The completed assembly is tough and impact resistant and smooth and attractive, with no rivets, screws or weld marks.

Because of the omnidirectional air flow and because of the lower temperature of the heated air and of the outer skin of the shell, the heater of this invention is safer than conventional heaters if tilted or tipped over. Conventional heaters must have safety devices to shut them off if tipped over because the very hot air blown from them can, if directed downwardly cause damage to such materials as polypropylene carpeting and can even cause fires. If the heater of this invention is tipped over and continues to operate, its omnidirectional air discharge will assure that most of the heated air will flow in directions other than downward and whatever air flows downwardly will not be so hot as to cause damage or fires.

FIG. 7 illustrates in cross section still another embodiment of the invention in which the heater is adapted to be placed in a corner of a room or other enclosed space. Shell 42 of FIG. 7 has a cross-sectional configuration in the form of a right triangle having walls 43 and 44 as the legs of the right triangle and wall 46 as the hypotenuse. Walls 43 and 44, which are inconvoluted heating strip and over its large surfaces,

then into and through a fan similar to fan 43 of FIG. 2 and then out of the shell through the top openings. When the heater is located in the corner of a room, the intake and exhaust openings in wall 46 can handle air from any part of the room; and vanes may be provided in the openings to produce a fan-shaped air flow into and out of the shell.

The heaters of this invention may vary considerably in capacity, depending on the job they are intended to perform and the wattage available. Small heating units of about 100 watts may be used for heating boats or for heating closets to avoid mildew. Units intended to heat residential rooms on household current will generally operate at wattages up to about 1,750, and even larger units can be utilized where there are large enclosed areas to be heated and higher current capacities available.

The heating strip may vary in width from about 2 inches to about 12 inches, and is preferably between about 3 and about 8 inches in width.

The heater of this invention is exceptionally compact. A cylindrical unit in accordance with FIGS. 1 to 3 having a capacity of 1,750 watts has a diameter of only 8 inches and is only 12 inches high. The heating strip in such a unit is 6 inches wide and 44 inches long and is wound in a spiral of 6 inch diameter having three turns.

It will be apparent to those skilled in the art that numerous modifications may be made without departing from the essence of this invention.

I claim:

l. A portable space heater comprising: an outer shell having an air inlet and an air outlet; an elongated heating strip including an electrically conductive layer having elongated electrodes near opposite edges thereof; mounting means carried by said shell and supporting said heating strip in convoluted form between said inlet and said outlet and out of contact with said shell, said mounting means including first and second open spider rings respectively supporting said opposite edges; interconnecting means between said rings maintaining said strip and rings in assembled relation; and a blower supported within said shell in open communication with said heating strip.

2. A portable space heater as defined in claim 1, in which said blower is mounted one of the rings adjacent the outlet with its suction side adjacent said strip.

3. A portable space heater as defined in claim 1, in which said spider rings each have a plurality of elongated spokes and each spoke has a plurality of transverse grooves for receiving the edges of said heating strip.

4. A portable space heater as defined in claim 1, in which said shell has a cylindrical side wall and top and bottom circular closures and in which said air inlet and said air outlet are respectively defined between the peripheries of said closures and opposite ends of said side wall.

5. A portable space heater as defined in claim 1, in which said heating strip has a resistance from about 20 to about 200 ohms per square and in which said heating strip is at least two inches wide with the air flowing along the surfaces between said sides.

6. A portable space heater as defined in claim 1, in which each spider ring has a hollow core at the center and in which said interconnecting means includes a hollow tube extending through openings in the hollow cores. 

1. A portable space heater comprising: an outer shell having an air inlet and an air outlet; an elongated heating strip including an electrically conductive layer having elongated electrodes near opposite edges thereof; mounting means carried by said shell and supporting said heating strip in convoluted form between said inlet and said outlet and out of contact with said shell, said mounting means including first and second open spider rings respectively supporting said opposite edges; interconnecting means between said rings maintaining said strip and rings in assembled relation; and a blower supported within said shell in open communication with said heating strip.
 2. A portable space heater as defined in claim 1, in which said blower is mounted one of the rings adjacent the outlet with its suction side adjacent said strip.
 3. A portable space heater as defined in claim 1, in which said spider rings each have a plurality of elongated spokes and each spoke has a plurality of transverse grooves for receiving the edges of said heating strip.
 4. A portable space heater as defined in claim 1, in which said shell has a cylindrical side wall and top and bottom circular closures and in which said air inlet and said air outlet are respectively defined between the peripheries of said closures and opposite ends of said side wall.
 5. A portable space heater as defined in claim 1, in which said heating strip has a resistance from about 20 to about 200 ohms per square and in which said heating strip is at least two inches wide with the air flowing along the surfaces between said sides.
 6. A portable space heater as defined in claim 1, in which each spider ring has a hollow core at the center and in which said interconnecting means includes a hollow tube extending through openings in the hollow cores. 